Method for acquiring parameter for dose correction of charged particle beam, charged particle beam writing method, and charged particle beam writing apparatus

ABSTRACT

A parameter acquiring method for dose correction of a charged particle beam includes writing evaluation patterns on a substrate coated with resist; writing, while varying writing condition, a peripheral pattern on a periphery of any different one of the evaluation patterns, after an ignorable time as to influence of resist temperature increase due to writing of an evaluation pattern concerned has passed; and calculating a parameter for defining correlation among a width dimension change amount of the evaluation pattern concerned, a temperature increase amount of the evaluation pattern concerned, and a backscatter dose reaching the evaluation pattern concerned, by using, under each writing condition, a width dimension of the evaluation pattern concerned, the temperature increase amount of the evaluation pattern concerned at each shot time, and the backscatter dose reaching the evaluation pattern concerned from each shot.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2015-225453 filed on Nov. 18,2015 in Japan, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate generally to a method foracquiring a parameter for correcting a dose of a charged particle beam,a charged particle beam writing method, and a charged particle beamwriting apparatus. More specifically, embodiments of the presentinvention relate, for example, to an apparatus and method that correctresist heating.

Description of Related Art

The lithography technique that advances miniaturization of semiconductordevices is extremely important as a unique process whereby patterns areformed in semiconductor manufacturing. In recent years, with highintegration of LSI, the line width (critical dimension) required forsemiconductor device circuits is decreasing year by year. For forming adesired circuit pattern on such semiconductor devices, a master or“original” pattern (also called a mask or a reticle) of high accuracy isneeded. Thus, the electron beam (EB) writing technique, whichintrinsically has excellent resolution, is used for producing such ahigh-precision master pattern.

FIG. 18 is a conceptual diagram explaining operations of avariable-shaped electron beam writing or “drawing” apparatus. Thevariable-shaped electron beam writing apparatus operates as describedbelow. A first aperture plate 410 has a quadrangular aperture 411 forshaping an electron beam 330. A second aperture plate 420 has a variableshape aperture 421 for shaping the electron beam 330 having passedthrough the aperture 411 of the first aperture plate 410 into a desiredquadrangular shape. The electron beam 330 emitted from a chargedparticle source 430 and having passed through the aperture 411 isdeflected by a deflector to pass through a part of the variable shapeaperture 421 of the second aperture plate 420, and thereby to irradiatea target object or “sample” 340 placed on a stage which continuouslymoves in one predetermined direction (e.g., x direction) during writing.In other words, a quadrangular shape that can pass through both theaperture 411 of the first aperture plate 410 and the variable shapeaperture 421 of the second aperture plate 420 is used for patternwriting in a writing region of the target object 340 on the stagecontinuously moving in the x direction. This method of forming a givenshape by letting beams pass through both the aperture 411 of the firstaperture plate 410 and the variable shape aperture 421 of the secondaperture plate 420 is referred to as a variable shaped beam (VSB)system.

With development of the optical lithography technology and shorterwavelengths due to EUV (extreme ultraviolet), the number of electronbeam shots required for mask writing is acceleratedly increasing. On theother hand, for ensuring the line width accuracy needed formicropatterning, it is aimed to reduce shot noise and pattern edgeroughness by making resist less sensitive and increasing the dose. Sincethe number of shots and the amount of dose increase limitlessly, thepattern writing time also increases limitlessly. Therefore, it is nowconsidered/examined to reduce the writing time by increasing the currentdensity.

However, if the substrate is irradiated with an increased amount ofirradiation energy as higher density electron beams in a short time,another problem occurs in that the substrate overheats resulting in aphenomenon called “resist heating” of changing the resist sensitivityand degrading the line width accuracy. To solve this problem, there isconsidered and examined a method (heating correction) of calculating,for each minimum deflection region in a deflection region, arepresentative temperature of the minimum deflection region concernedbased on heat transfer from other minimum deflection regions writtenprior to the current one, and of modulating the dose by using therepresentative temperature (refer to Japanese Patent ApplicationLaid-open (JP-A) No. 2012-069675).

On the other hand, in the electron beam writing, when writing a circuitpattern by irradiating a mask, coated with resist, with electron beams,a phenomenon called a “proximity effect” occurs due to backscattering ofthe electron beams penetrating the resist film, reaching the layerthereunder to be reflected, and entering the resist film again. Thereby,a dimensional change occurs, that is, a written pattern is deviated froma desired dimension. In order to avoid this phenomenon, a proximityeffect correction operation that suppresses such dimensional change bymodulating the dose is for example performed in the writing apparatus.

The dose modulation against the resist heating described above isperformed in consideration of the temperature at the time of an electronbeam shot of interest (target shot, shot concerned). Therefore,temperature is not considered with respect to calculation for correctingthe proximity effect generated by backscattering by another shot at theperipheral position different from that of the shot of interest (targetshot). Accordingly, when the heating effect of the backscatter is large,there is a problem in that the correction error is large in theconventional calculation model. Therefore, it is desirable to correctthe heating effect with respect to a backscattered electron at the timeof exposure. However, conventionally, a sufficient correction method hasnot been established.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method for acquiringa parameter for correcting a dose of a charged particle beam includeswriting, using a charged particle beam, a plurality of evaluationpatterns on a substrate coated with resist; writing, under each writingcondition while varying writing condition for each of the plurality ofevaluation patterns, a peripheral pattern according to a correspondingwriting condition on a periphery of any different one of the pluralityof evaluation patterns by using a plurality of shots of the chargedparticle beam, after time that can be disregarded with respect toinfluence of temperature increase of the resist due to writing of anevaluation pattern concerned of the plurality of evaluation patterns haspassed; measuring, under the each writing condition, a width dimensionof the evaluation pattern concerned, on whose periphery the peripheralpattern has been written; calculating, under the each writing condition,a backscatter dose reaching the evaluation pattern concerned from eachshot of the plurality of shots; calculating, under the each writingcondition, a temperature increase amount of the evaluation patternconcerned, which is increased due to heat transferred from at least oneshot previous to a shot concerned in the plurality of shots, at eachshot time of the plurality of shots; and calculating a correlationparameter for defining a correlation among a width dimension changeamount of the evaluation pattern concerned, the temperature increaseamount of the evaluation pattern concerned, and the backscatter dosereaching to the evaluation pattern concerned, by using a width dimensionof the evaluation pattern concerned under the each writing condition,the temperature increase amount of the evaluation pattern concerned atthe each shot time under the each writing condition, and the backscatterdose reaching the evaluation pattern concerned from the each shot underthe each writing condition, and outputting the correlation parameter.

According to another aspect of the present invention, a charged particlebeam writing method includes extracting information on a type of resistcoated on a writing target substrate; reading out a correspondingcorrelation parameter which corresponds to the resist of an extractedtype from a storage device which stores, for each type of the resist, acorrelation parameter for a width dimension change amount of a figurepattern, a temperature increase amount of the figure pattern, and abackscatter dose reaching the figure pattern, and calculating the widthdimension change amount of the figure pattern by using the correlationparameter when writing the figure pattern under a predetermined writingcondition by using a charged particle beam; determining, using the widthdimension change amount, whether it is necessary to correct a dose ofthe charged particle beam when writing, under the predetermined writingcondition, the figure pattern by using the charged particle beam;calculating a correction coefficient for correcting the dose of thecharged particle beam for writing the figure pattern when it isdetermined that correction of the dose is needed; correcting, using thecorrection coefficient, the dose of the charged particle beam forwriting the figure pattern; and writing, under the predetermined writingcondition, the figure pattern on the writing target substrate by usingthe charged particle beam of the dose having been corrected.

According to yet another aspect of the present invention, a chargedparticle beam writing apparatus includes an extraction processingcircuitry configured to extract information on a type of resist coatedon a writing target substrate; a storage device configured to store, foreach type of the resist, a correlation parameter for a width dimensionchange amount changed from a design dimension of a figure pattern, atemperature increase amount of the figure pattern, and a backscatterdose reaching the figure pattern; a width dimension change amountcalculation processing circuitry configured to read out a correspondingcorrelation parameter which corresponds to an extracted type of theresist from the storage device, and to calculate the width dimensionchange amount of the figure pattern by using the correlation parameterin a case of writing the figure pattern under a predetermined writingcondition by using a charged particle beam; a determination processingcircuitry configured to determine, using the width dimension changeamount, whether it is necessary to correct a dose of the chargedparticle beam in the case of writing, under the predetermined writingcondition, the figure pattern by using the charged particle beam; acorrection coefficient calculation processing circuitry configured tocalculate a correction coefficient for correcting the dose of thecharged particle beam for writing the figure pattern in a case where itis determined that correction of the dose is needed; a correctionprocessing circuitry configured to correct, using the correctioncoefficient, the dose of the charged particle beam for writing thefigure pattern; and a writing mechanism configured to include a stagefor mounting the writing target substrate thereon, an emission sourcefor emitting charged particle beams, and a deflector for deflecting thecharged particle beams, and to write, under the predetermined writingcondition, the figure pattern on the writing target substrate by usingthe charged particle beam of the dose having been corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing a configuration of a writingapparatus according to a first embodiment;

FIG. 2 is a conceptual diagram for explaining each region according tothe first embodiment;

FIGS. 3A to 3C show examples of a backscattering amount and atemperature increase amount at a width dimension measurement position ina comparative example (1) to the first embodiment;

FIGS. 4A to 4D show examples of a backscattering amount and atemperature increase amount at a width dimension measurement position ina comparative example (2) to the first embodiment;

FIG. 5 is a flowchart showing main steps of a method for acquiring aparameter for correcting the dose of an electron beam according to thefirst embodiment;

FIGS. 6A and 6B show an example of an evaluation method and atemperature increase amount at a width dimension measurement positionaccording to the first embodiment;

FIGS. 7A and 7B show an example of a relation between a width dimensionof an evaluation pattern and a settling time according to thecomparative example (2) to the first embodiment;

FIGS. 8A and 8B show an example of a relation between a width dimensionof an evaluation pattern and a settling time according to the firstembodiment;

FIGS. 9A and 9B show an example of a calculation model for calculating abackscatter dose which reaches to the shot position of interestaccording to the first embodiment;

FIG. 10 shows an example of a calculation model for calculating atemperature increase amount at a shot position of interest, which isincreased due to heat transferred from another shot, according to thefirst embodiment;

FIG. 11 shows an example of a model of correlation according to thefirst embodiment;

FIGS. 12A to 12C show another example of an evaluation pattern and aperipheral pattern according to the first embodiment;

FIGS. 13A and 13B show another example of the evaluation pattern and theperipheral pattern according to the first embodiment;

FIGS. 14A and 14B show another example of the evaluation pattern and theperipheral pattern according to the first embodiment;

FIGS. 15A to 15F show an example of a width dimension depending on thetype of resist according to the first embodiment;

FIG. 16 is a flowchart showing main steps of a writing method accordingto the first embodiment;

FIG. 17 shows an example of a relation between the width dimension andthe dose according to the first embodiment; and

FIG. 18 is a conceptual diagram explaining operations of avariable-shaped electron beam writing apparatus.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention provides a method of acquiring aparameter for performing dose correction for heating effect ofbackscatter, or an apparatus and method that can perform writing aftercorrecting the dose by using such a parameter.

In the embodiments below, there will be described a configuration inwhich an electron beam is used as an example of a charged particle beam.The charged particle beam is not limited to the electron beam, and othercharged particle beam such as an ion beam may also be used. Moreover, awriting apparatus of a variably shaped beam type will be described as anexample of a charged particle beam apparatus.

First Embodiment

FIG. 1 is a conceptual diagram showing a configuration of a writingapparatus according to the first embodiment. As shown in FIG. 1, awriting apparatus 100 includes a writing unit 150 and a control unit160. The writing apparatus 100 is an example of a charged particle beamwriting apparatus. Particularly, it is an example of a writing apparatusof a variably shaped beam (VSB) type. The writing unit 150 includes anelectron optical column 102 and a writing chamber 103. In the electronoptical column 102, there are arranged an electron gun 201, anillumination lens 202, a blanking deflector (blanker) 212, a blankingaperture member 214, a first shaping aperture member 203, a projectionlens 204, a deflector 205, a second shaping aperture member 206, anobjective lens 207, a main deflector 208, and a sub deflector 209. Inthe writing chamber 103, there is arranged an XY stage 105 which ismovable at least in the x-y directions. On the XY stage 105, there isplaced a target object or “sample” 101 (substrate) which serves as awriting target coated with resist. The target object 101 may be anexposure mask, a silicon wafer, and the like used for manufacturingsemiconductor devices. Alternatively, on the XY stage 105, there isplaced an evaluation substrate 300 (substrate) which serves as anevaluation target coated with resist. The evaluation substrate 300 maybe an exposure mask, a silicon wafer, and the like. The mask may be amask blank. On the glass substrate of the mask blank, a light-shieldingfilm of such as chromium (Cr), and a resist film are laminated in thisorder. A plurality of evaluation substrates 300 whose resist types aredifferent are used.

The control unit 160 includes a control computer unit 110, a memory 112,a deflection control circuit 120, DAC (digital-analog converter)amplifier units 130, 132 and 134 (deflection amplifiers), and storagedevices 140, 142, 144, 146, and 148 such as magnetic disk drives. Thecontrol computer unit 110, the deflection control circuit 120, and thestorage devices 140, 142, 144, 146, and 148 are connected with eachother through a bus (not shown). The DAC amplifier units 130, 132, and134 are connected to the deflection control circuit 120. The DACamplifier unit 130 is connected to the blanking deflector 212. The DACamplifier unit 132 is connected to the sub deflector 209, and the DACamplifier unit 134 is connected to the main deflector 208.

In the control computer unit 110, there are arranged a writing conditionsetting unit 50, a shot data generation unit 52, a determination unit53, a dose calculation unit 54, a setting unit 56, a resist informationextraction unit 58, a backscatter dose calculation unit 60, atemperature increase amount calculation unit 62, a width change amount(ΔCD) calculation unit 64, a determination unit 66, a correctioncoefficient calculation unit 68, a correction unit 70, a determinationunit 72, a writing control unit 74, a ΔCD calculation unit 76, and acorrelation parameter calculation unit 78. Each “ . . . unit” includes aprocessing circuitry. As the processing circuitry, for example, anelectric circuit, computer, processor, circuit board, quantum circuit,or semiconductor device may be used. The processing circuitry includedin each “ . . . unit” may be a common processing circuitry (sameprocessing circuitry), or different processing circuitries (separateprocessing circuitries). Input data required in the control computerunit 110, and calculated results are stored in the memory 112 each time.

Writing data is input from the outside of the writing apparatus 100, andstored in the storage device 140. Writing condition information andresist information are input from the outside of the writing apparatus100, and stored in the storage device 142. Information on a correlationparameter for each resist type is stored in the storage device 144. Theinformation on the correlation parameter for each resist type may beinput from the outside of the writing apparatus 100, or calculatedinside the writing apparatus 100. Chip A data and chip B data of anevaluation pattern are input from the outside of the writing apparatus100, and stored in the storage device 146.

FIG. 1 shows configuration elements necessary for describing the firstembodiment. It should be understood that other configuration elementsgenerally necessary for the writing apparatus 100 may also be includedtherein.

FIG. 2 is a conceptual diagram for explaining each region according tothe first embodiment. In FIG. 2, a writing region 10 of the targetobject 101 is virtually divided into a plurality of strip-shaped striperegions 20 by the width dimension that can be deflected, for example, inthe y direction by the main deflector 208. Further, each of the striperegions 20 is virtually divided into a plurality of mesh-like subfields(SFs) 30 (small regions) by the size that can be deflected by the subdeflector 209. Then, a shot figure is written at each shot position 42in each SF 30.

A digital signal for blanking control is output from the deflectioncontrol circuit 120 to the DAC amplifier unit 130. Then, in the DACamplifier unit 130, the digital signal is converted to an analog signal,and amplified to be applied as a deflection voltage to the blankingdeflector 212. An electron beam 200 is deflected by this deflectionvoltage so that a beam of each shot may be formed.

A digital signal for controlling main deflection is output from thedeflection control circuit 120 to the DAC amplifier unit 134. Then, inthe DAC amplifier unit 134, the digital signal is converted to an analogsignal and amplified to be applied as a deflection voltage to the maindeflector 208. By this deflection voltage, the electron beam 200 isdeflected, and thereby each shot beam is deflected to a referenceposition in a predetermined subfield (SF) obtained by virtually dividinginto mesh-like regions.

A digital signal for controlling sub deflection is output from thedeflection control circuit 120 to the DAC amplifier unit 132. Then, inthe DAC amplifier unit 132, the digital signal is converted to an analogsignal and amplified to be applied as a deflection voltage to the subdeflector 209. By this deflection voltage, the electron beam 200 isdeflected, and thereby each shot beam is deflected to each shot positionin a predetermined subfield (SF) obtained by virtually dividing intomesh-like regions.

The writing apparatus 100 performs writing processing in each striperegion 20 by using a multiple stage deflector of a plurality of stages.Here, as an example, a two-stage deflector composed of the maindeflector 208 and the sub deflector 209 is used. However, it is notlimited to the two-state deflector, a single stage deflector or amultiple stage deflector of three or more stages may also be used. Whilethe XY stage 105 is continuously moving in the −x direction, forexample, writing is performed in the x direction in the first striperegion 20. After the writing has been finished in the first striperegion 20, continuously writing is performed in the same direction or inthe opposite direction in the second stripe region 20. Then, in the sameway, writing is performed in the third and subsequent stripe regions 20.The main deflector 208 (first deflector) sequentially deflects theelectron beam 200 to a reference position A of the SF 30 such that themovement of the XY stage 105 is followed. The sub deflector 209 (seconddeflector) deflects the electron beam 200 from the reference position Aof each SF 30 to the shot position 42 of an irradiating beam in the SF30 concerned. Thus, the sizes of the deflection regions of the maindeflector 208 and the sub deflector 209 are different from each other.The SF 30 is the smallest deflection region in the deflection regions ofthe multiple stage deflector.

In the case where a shot position of interest (shot position concerned,target shot position) exists in the range of influence of the proximityeffect of a peripheral shot, the shot position of interest is exposed bya backscattered electron generated by the beam irradiation of theperipheral shot, at substantially the same time with the beamirradiation of the peripheral shot. Therefore, in the conventionalproximity effect correction, calculation is performed considering thatthe dose of the backscattered electron is accumulated at the shotposition of interest. Then, it is supposed that temperature affects notonly when a shot of interest (target shot) is performed to the shotposition of interest (shot position concerned) but also when the shotposition of interest is exposed by the backscattered electron generatedby other shots. However, in the conventional proximity effectcorrection, the influence of temperature at the time of the shotposition of interest being exposed by the backscattered electron has notbeen considered. Therefore, when the heating effect of backscatter islarge, the correction error is large in the conventional calculationmodel. Then, it is desirable to grasp (measure) the amount ofdimensional change due to the heating effect accompanied by exposure ofa backscattered electron while separating it from the amount ofdimensional change due to other causes.

FIGS. 3A to 3C show examples of a backscattering amount and atemperature increase amount at a width dimension measurement position ina comparative example (1) to the first embodiment. The example of FIG.3A shows the case of writing a line-shaped evaluation pattern 12 at theposition (width dimension measurement position) where a width dimension(CD) is measured, after writing a peripheral pattern 14 on the peripheryof the position where the CD is measured, on the evaluation substratecoated with resist, by using a plurality of shots of electron beams. Theexample of FIG. 3A also shows the case where the evaluation pattern 12is formed by connecting a plurality of quadrangular shot figures in aline to be a line pattern. On the other hand, the peripheral pattern 14is a so-called solid pattern that fills the peripheral region. Theperipheral pattern 14 and the evaluation pattern 12 are defined in onechip data, and each shot is performed continuously with having a waitingtime between shots being a set stabilization time (settling time). Here,the case of setting the waiting time between shots to be a shortsettling time (short settling), and the case of setting the waiting timebetween shots to be a long settling time (long settling) are evaluated.In addition, for example, a central shot figure of quadrangular shotfigures forming the evaluation pattern 12 is set as a CD measurementposition.

In that case, in FIG. 3B, the ordinate axis represents a doseirradiating (exposing) the CD measurement position, and the abscissaaxis represents shot numbers in the order of shot in writing a pluralityof shot figures forming the evaluation pattern 12 and the peripheralpattern 14. Since the writing starts from the peripheral pattern 14,FIG. 3B shows the dose of an electron irradiating the CD measurementposition in the backscattered electrons generated by the shot for theperipheral pattern 14 at each beam shot time in writing a plurality ofshot figures forming the peripheral pattern 14. Then, FIG. 3B shows thedose of a beam itself (forward scattering) of a shot in finally writinga plurality of shot figures forming the evaluation pattern 12. Since thedose of a beam itself (forward scattering) of each shot for theperipheral pattern 14 does not change even if the settling time betweenshots differs, as shown in FIG. 3B, the dose (backscatter dose) of abackscattered electron is the same value regardless of the settling timebetween shots.

On the other hand, the situation of the temperature at the CDmeasurement position is different from what is described above. Thetemperature at the CD measurement position of the evaluation substratechanges due to transferred heat of the temperature increased by a beampreviously shot at another position. As shown in FIG. 3C, in the case ofthe settling time being short, the temperature at the CD measurementposition of the evaluation substrate continues to increase because,before the temperature having been increased due to heat transferredfrom a previous shot has fallen by heat release (diffusion), other heatis transferred from a next shot. On the other hand, in the case of thesettling time being long, the increase of the temperature at the CDmeasurement position of the evaluation substrate can be suppressedbecause, after the temperature having been increased due to heattransferred from a previous shot has fallen by heat release (diffusion),other heat is transferred from a next shot. Therefore, the resisttemperature at the time of finally writing a plurality of shot figuresforming the evaluation pattern 12 is different between the cases of theshort settling time and the long settling time. Accordingly, resistresolution by the dose of a shot at the time of writing a plurality ofshot figures forming the evaluation pattern 12 is larger in the case ofthe short settling time and therefore the high resist temperature.Therefore, even if the width dimension (CD) measured at a CD measurementposition of the finally obtained evaluation pattern 12 in the case ofthe short settling time is compared with that in the case of the longsettling time, it is difficult to separate the amount of dimensionalchange due to a heating effect accompanied by exposure of abackscattered electron from the amount of dimensional change due toother causes.

FIGS. 4A to 4D show examples of a backscattering amount and atemperature increase amount at a width dimension measurement position ina comparative example (2) to the first embodiment. The example of FIG.4A shows the case of writing the peripheral pattern 14 on the peripheryof the position (width dimension measurement position) where the widthdimension (CD) is measured, on the evaluation substrate coated withresist, by using a plurality of shots of electron beams, after writingthe line-shaped evaluation pattern 12 at the position where the CD ismeasured. The writing order of FIG. 4A is an example of a reversewriting order to that of FIG. 3A. Also in FIG. 4A, the peripheralpattern 14 and the evaluation pattern 12 are defined in one chip data,and each shot is performed continuously with having a waiting timebetween shots being a set stabilization time (settling time). In theexample of FIG. 4A, similarly to FIG. 3A, the case of setting thewaiting time between shots to be a short settling time (short settling),and the case of setting the waiting time between shots to be a longsettling time (long settling) are evaluated. In addition, for example, acentral shot figure of quadrangular shot figures forming the evaluationpattern 12 is set as a CD measurement position.

In that case, in FIG. 4B, the ordinate axis represents a doseirradiating (exposing) the CD measurement position, and the abscissaaxis represents shot numbers in the order of shot in writing a pluralityof shot figures forming the evaluation pattern 12 and the peripheralpattern 14. FIG. 4B shows the dose of a beam itself (forward scattering)of a shot in firstly writing a plurality of shot figures forming theevaluation pattern 12. Then, subsequently, FIG. 4B shows the dose of anelectron irradiating the CD measurement position in the backscatteredelectrons generated by the shot for the peripheral pattern 14 at eachbeam shot time in writing a plurality of shot figures forming theperipheral pattern 14. Since the dose of a beam itself (forwardscattering) of each shot for the peripheral pattern 14 does not changeeven if the settling time between shots differs, as shown in FIG. 4B,the dose (backscatter dose) of a backscattered electron is the samevalue regardless of the settling time between shots.

On the other hand, the situation of the temperature at the CDmeasurement position is different from what is described above. Sincethe peripheral pattern 14 is subsequently written as shown in FIG. 4C,when compared with FIG. 3C, there is no resist temperature increase atthe time of writing a plurality of shot figures forming the evaluationpattern 12 due to heat transferred from each shot for the peripheralpattern 14. However, in the case of the short settling time, since thewriting of the peripheral pattern 14 is started before the resisttemperature having been increased due to a plurality of shots forforming the evaluation pattern 12 has fallen by heat release(diffusion), the resist temperature at the time of backscatteredelectrons, generated by each shot for the peripheral pattern 14,exposing the CD measurement position is different between the cases ofthe short settling time and the long settling time. Accordingly, resistresolution by the dose of a backscattered electron at the CD measurementposition at writing start of the peripheral pattern 14 is larger in thecase of the short settling time and therefore the high resisttemperature.

Furthermore, as shown in FIG. 4D, in the case of the short settlingtime, the resist temperature at the time of a shot 11 has increased dueto heat transferred from a shot 13 of a beam irradiation applied beforethe shot 11 at the CD measurement position when forming the evaluationpattern 12. Therefore, the resist temperature at the time of writing aplurality of shot figures forming the evaluation pattern 12 is differentbetween the cases of the short settling time and the long settling time.Accordingly, resist resolution by the dose of a shot in writing a shotfigure forming the evaluation pattern 12 at the CD measurement positionis larger in the case of the short settling time and therefore the highresist temperature.

Therefore, even if the width dimension (CD) measured at a CD measurementposition of the finally obtained evaluation pattern 12 in the case ofthe short settling time is compared with that in the case of the longsettling time, the amount of dimensional change due to a heating effectaccompanied by exposure of a backscattered electron is not separatedfrom the amount of dimensional change due to other causes.

Then, according to the first embodiment, the amount of dimensionalchange due to a heating effect accompanied by exposure of abackscattered electron is separated from the amount of dimensionalchange due to other causes by performing measurement as described below.

FIG. 5 is a flowchart showing main steps of a method for acquiring aparameter for correcting the dose of an electron beam according to thefirst embodiment. As shown in FIG. 5, the method for acquiring aparameter for correcting the dose of an electron beam according to thefirst embodiment executes a series of steps: a writing condition settingstep (S102), an evaluation pattern writing step (S104), a peripheralpattern writing step (S106), a determination step (S108), a writingcondition change step (S110), a width dimension (CD) measurement step(S112), a width change amount (ΔCD) calculation step (S114), abackscatter dose calculation step (S116), a temperature increase amountcalculation step (S118), and a correlation parameter calculation step(S120).

In the writing condition setting step (S102), the writing conditionsetting unit 50 sets writing conditions for writing the chip A and thechip B to the writing apparatus 100 (writing control unit 74, forexample). As an example of the writing conditions, settling time betweena plurality of shots can be cited. A long settling time is set in thechip A. For example, the time is set to be 800 ns. In the chip A, thesettling time being a waiting time between shots should be set such thata shot of interest starts after the temperature having been increaseddue to heat transferred from a peripheral shot has diffused. Next, thesettling time between a plurality of shots for forming a pattern of thechip B is set. In the chip B, a plurality of settling times from a shortsettling time to a long settling time are determined in advance. Forexample, 20 ns, 50 ns, 100 ns, 300 ns, and 800 ns are determined inadvance. Then, one of a plurality of settling times is set. For example,20 ns is set. As will be described later, in the chip B, a pattern ofthe chip B is written a plurality of times while varying the settlingtime per pattern of the chip B. The writing condition setting unit 50sets other writing conditions. For example, a dose, the number of passes(multiplicity) of multiple writing, the order of writing of shots, themaximum shot size, etc. can be cited.

FIGS. 6A and 6B show an example of an evaluation method and atemperature increase amount at a width dimension measurement positionaccording to the first embodiment. As shown in FIG. 6A, according to thefirst embodiment, the evaluation pattern 12 and the peripheral pattern14 are defined in different chips. In the example of FIG. 6A, theevaluation pattern 12 is defined in the chip A, and the peripheralpattern 14 is defined in the chip B. In the example of FIG. 6A, oneevaluation pattern 12 being a line pattern is arranged in one SF 30, forexample. Then, while centering the SF 30, the peripheral pattern 14composed of what is called solid patterns for writing the whole area isarranged in each of a plurality of SFs 30 in an influence range 15 ofthe proximity effect 15. Also, with respect to the SF 30 in which theevaluation pattern 12 is arranged, it is preferable that solid patternsare arranged in a remaining region while having a space to theevaluation pattern 12. The space can be any size as long as the widthdimension of the evaluation pattern 12 can be measured by a dimensionmeasuring instrument. For example, the space may be several times themaximum shot size, such as around five times. As shown in FIG. 6A,first, writing of the chip A in which the evaluation pattern 12 isdefined is performed. Then, changing the writing target chip to the chipB from the chip A, the chip B in which the peripheral pattern 14 isdefined is written on the periphery of the evaluation pattern 12. Whilevarying the writing conditions (the settling time in this case) of thechip B, combining the writing of the chip A and the writing of the chipB is performed a plurality of times. Specifically, it is describedbelow.

In the evaluation pattern writing step (S104), the writing unit 150controlled by the writing control unit 74 writes, using the electronbeam 200, a plurality of evaluation patterns 12 defined in the chip A,on the evaluation substrate 300 coated with resist. Here, the evaluationpattern 12 is written at each separated position on the evaluationsubstrate 300. For example, the evaluation pattern 12 is written inevery several stripe regions 20. The distance between the adjacent twoevaluation patterns 12 is preferably the distance by which the resisttemperature at the position where the evaluation pattern 12 of interestis written does not increase by the heat transferred from the beam shotfor writing the other evaluation pattern 12 of the two, and theevaluation pattern 12 of interest is located out of the influence rangeof the proximity effect of the beam shot for writing the otherevaluation pattern 12. That is, when writing the evaluation pattern 12of interest, it is necessary to keep the distance by which no influenceof writing of the other evaluation pattern 12 of the two is given. Here,although there has been described the case of defining a plurality ofevaluation patterns 12 in the chip A, and writing a plurality ofevaluation patterns 12 in one evaluation substrate 300 while changingthe writing position, it is not limited thereto. It is also preferableto write the evaluation pattern 12 on each of different evaluationsubstrates 300.

In order to write a plurality of evaluation patterns 12 defined in thechip A, the shot data generation unit 52 reads chip data of the chip Afrom the storage device 146, performs multiple stages of data conversionprocessing, and divides the evaluation pattern 12 defined in the chip Ainto a plurality of shot figures which can be written by the writingapparatus 100. Then, shot data defining a figure type, a coordinateposition, size, etc. for each shot figure is generated. The generatedshot data is stored in the storage device 148. The shot data is output,under the control of the writing control unit 74, to the deflectioncontrol circuit 120, various deflection data is generated, and writingis performed by the writing unit 150 controlled by the writing controlunit 74.

In the peripheral pattern writing step (S106), the writing unit 150controlled by the writing control unit 74 writes, using a plurality ofshots of the electron beam 200, the peripheral pattern 14 defined in thechip B according to corresponding writing conditions, on the peripheryof any different one of a plurality of evaluation patterns 12 after thetime that can be disregarded with respect to the influence of resisttemperature increase due to writing of the evaluation pattern 12concerned has passed. Here, for example, the peripheral pattern 14 iswritten with waiting time between shots whose settling time is set to be20 ns on the periphery of one of a plurality of evaluation patterns 12.

In the determination step (S108), the determination unit 53 determineswhether the peripheral pattern writing step (S106) under all thescheduled predetermined writing conditions has been completed. Here, forexample, it is determined whether the peripheral pattern writing step(S106) has been completed with respect to all of a plurality of settlingtimes prepared for writing the peripheral pattern 14. When theperipheral pattern writing step (S106) under all the scheduledpredetermined writing conditions has been completed, it proceeds to thewidth dimension (CD) measurement step (S112). When the peripheralpattern writing step (S106) under all the scheduled predeterminedwriting conditions has not been completed yet, it proceeds to thewriting condition change step (S110).

In the writing condition change step (S110), the writing conditionsetting unit 50 changes the writing conditions for writing the chip Bhaving been set in the writing apparatus 100. For example, the settlingtime is changed to 50 ns from 20 ns. Then, returning to the peripheralpattern writing step (S106), steps from the peripheral pattern writingstep (S106) to the writing condition change step (S110) are repeateduntil it is determined that the peripheral pattern writing step (S106)under all the scheduled predetermined writing conditions has beencompleted. In that case, under each writing condition, the evaluationpattern 12 around which the peripheral pattern 14 is written on theperiphery is changed to another evaluation pattern 12.

As described above, according to the first embodiment, while varying thewriting conditions for each evaluation pattern 12, under each writingcondition, the peripheral pattern 14 defined in the chip B according tocorresponding writing conditions is written on the periphery of anydifferent one of a plurality of evaluation patterns 12 by using aplurality of shots of the electron beam 200, after the time that can bedisregarded with respect to the influence of resist temperature increasedue to writing of the evaluation pattern 12 concerned has passed.

In order to write the peripheral pattern 14 defined in the chip B, theshot data generation unit 52 reads chip data of the chip B from thestorage device 146, performs multiple stages of data conversionprocessing, and divides the peripheral pattern 14 defined in the chip Binto a plurality of shot figures which can be written by the writingapparatus 100. Then, shot data defining a figure type, a coordinateposition, size, etc. for each shot figure is generated. The generatedshot data is stored in the storage device 148. The shot data is output,under the control of the writing control unit 74, to the deflectioncontrol circuit 120, various deflection data is generated, and writingis performed by the writing unit 150 controlled by the writing controlunit 74. Due to the time of such data processing, by the time ofstarting to write the peripheral pattern 14, the time that can bedisregarded with respect to the influence of resist temperature increasedue to writing of the evaluation pattern 12 concerned has passed.According to the first embodiment, by dividing into the chip A and thechip B, the influence of the resist temperature increase due to writingthe evaluation pattern 12 can be eliminated when the backscatteredelectron resulting from writing of the peripheral pattern 14 exposes thedimension measurement position of the evaluation pattern 12.

As shown in FIG. 6B, since the chip is changed and then the peripheralpattern 14 is written, that is, since writing of the peripheral pattern14 is started after the resist temperature having been increased due toa plurality of shots for forming the evaluation pattern 12 has fallen byheat release (diffusion), it becomes possible not to affect the resisttemperature at a CD measurement position exposed by backscatteredelectrons generated by each shot for the peripheral pattern 14.

Therefore, the resist temperature of a CD measurement position at thetime of backscattered electrons exposing the CD measurement position canbe compared between the cases of the short settling time and the longsettling time in the state in which other factors are eliminated. Thedose of a beam itself (forward scattering) of a shot in writing aplurality of shot figures forming the evaluation pattern 12, and thedose irradiating a CD measurement position in backscattered electrons,generated by the shot for the peripheral pattern 14, at the time of eachbeam shot in writing a plurality of shot figures forming the peripheralpattern 14 are the same as those in FIG. 4B. In other words, the dose ofbackscattered electrons does not depend on the waiting time (settlingtime) between shots. Therefore, it is the same as that in FIG. 4B.

Furthermore, according to the first embodiment, since the evaluationpattern 12 is formed by being written with each shot whose settling timeis long, even if the resist temperature at the CD measurement positionincreases due to heat transferred from the shot 13 of a beam irradiationapplied before the shot 11 at the CD measurement position shown in FIG.4D, the shot 11 to the CD measurement position can be performed afterthe resist temperature has fallen by heat release (diffusion).Therefore, when the width dimension CD measured at the CD measurementposition of the evaluation pattern 12 finally obtained is comparedbetween the cases of the short settling time and the long settling time,the dimension difference can be measured as a dimension change amountresulting from a heating effect accompanied by exposure of abackscattered electron, while separating it from the amount ofdimensional change due to other causes.

The evaluation substrate 300, on which several combinations of theevaluation pattern 12 and the peripheral pattern 14 whose writingconditions are different from each other are written, is taken out fromthe writing apparatus 100 to be developed. Thereby, a resist pattern ofa plurality of combinations of the evaluation pattern 12 and theperipheral pattern 14 whose writing conditions are different from eachother is formed. Using this resist pattern as a mask, a light shieldingfilm is etched, and then, the resist material is removed by ashing etc.,so that a pattern group of several combinations of the evaluationpattern 12 and the peripheral pattern 14 whose writing conditions aredifferent from each other is formed by a light shielding film.

In the width dimension (CD) measurement step (S112), the width dimensionCD of the evaluation pattern 12 around which the peripheral patterns 14are written is measured using a dimension measuring instrument (notshown), under each writing condition.

In the width change amount (ΔCD) calculation step (S114), the ΔCDcalculation unit 76 calculates a width change amount (ΔCD) of theevaluation pattern 12, under each writing condition.

FIGS. 7A and 7B show an example of a relation between a width dimensionof an evaluation pattern and a settling time according to thecomparative example (2) to the first embodiment. FIG. 7A is the same asFIG. 4A. That is, in the example of FIG. 7A, the evaluation pattern 12and the peripheral pattern 14 are defined in the same chip, and theperipheral pattern 14 is written on the periphery of the position (widthdimension measurement position) where the width dimension (CD) ismeasured, on the evaluation substrate coated with resist, by using aplurality of shots of electron beams, after writing the line-shapedevaluation pattern 12 at the position where the CD is measured, andcontinuously after the set settling time has passed. Such writing issimilarly performed while changing the settling time. Consequently, asshown in FIG. 7B, the width dimension CD at the width dimensionmeasurement position finally acquired changes for each settling time.The width dimension CD written with the settling time of, for example,300 ns or more within which the width dimension CD converges can beregarded as a value in the case of there being no dimension changeamount due to a heating effect. The width dimension CD in the case ofthere being no dimension change amount due to a heating effect becomeslarger as the settling time becomes shorter. The difference of the widthdimension CD between the case of no dimension change and the case of CDbecoming larger is a width dimension change amount (ΔCD) for eachsettling time. However, as described above, in the method of thecomparative example (2), what changes is not only the amount ofdimensional change due to a heating effect accompanied by exposure ofbackscattered electrons. Therefore, it is difficult to calculate, fromthe result described above, the amount of dimensional change due to aheating effect accompanied by exposure of a backscattered electron.

FIGS. 8A and 8B show an example of a relation between a width dimensionof an evaluation pattern and a settling time according to the firstembodiment. FIG. 8A is the same as FIG. 6A. That is, the evaluationpattern 12 and the peripheral pattern 14 are individually defined indifferent chips, and the peripheral pattern 14 defined in chip B iswritten on the periphery of the position (width dimension measurementposition) where the width dimension (CD) is measured, on the evaluationsubstrate 300 coated with resist, by using a plurality of shots ofelectron beams, after the line-shaped evaluation pattern 12 defined inchip A is written at the position where the CD is measured. Such writingis similarly performed while changing the settling time. Consequently,as shown in FIG. 8B, the width dimension CD at the width dimensionmeasurement position finally acquired changes for each settling time.The width dimension CD written with the settling time of, for example,300 ns or more within which the width dimension CD converges can beregarded as a value in the case of there being no dimension changeamount due to a heating effect. The width dimension CD in the case ofthere being no dimension change amount due to a heating effect becomeslarger as the settling time becomes shorter. The difference of the widthdimension CD between the case of no dimension change and the case of CDbecoming larger is a width dimension change amount (ΔCD) for eachsettling time. As understood from that ΔCD of FIG. 8B is smaller thanΔCD of FIG. 7B, the ΔCD of FIG. 8B is shown such that change of theamount of dimensional change due to a heating effect accompanied byexposure of a backscattered electron is separated from the amount ofdimensional change due to other causes. Therefore, based on such result,it is possible to calculate the amount of dimensional change due to aheating effect accompanied by exposure of a backscattered electron.

In the backscatter dose calculation step (S116), the backscatter dosecalculation unit 60 calculates, under each writing condition, abackscatter dose which reaches to the evaluation pattern 12 concernedfrom each of a plurality of shots for forming the peripheral pattern 14.

FIGS. 9A and 9B show an example of a calculation model for calculating abackscatter dose which reaches to the shot position of interest (shotposition concerned) according to the first embodiment. The example ofFIG. 9A shows an incident dose (forward scattered electron) and abackscattered electron in the case where an electron beam is applied toa peripheral shot position j being different from the position (xi, yi)of a target shot position i. The dose of a forward scattered electron isshown by a quadrangle. The dose of a backscattered electron is shown bythe profile of a distribution function. The example of FIG. 9B shows anexample of a positional relation between the position (xj, yj) of theperipheral shot position j and the position (xi, yi) of the target shotposition i. The example of FIG. 9B shows the case where, when theperipheral shot position j is irradiated with the shot j of beam size(aj×bj), the coordinates (xi, yi) of the target shot position i exist inthe backscatter radius σ (influence radius of proximity effect)centering on the peripheral shot position j. In that case, thebackscatter dose dj by the j-th shot, which reaches to the target shotposition i, can be defined by the equation (1) described below, usingthe position (xi, yi) of the i-th shot, the position (xj, yj) of thej-th shot, the beam dose Dj of the j-th shot, the backscatter rate η,the backscatter radius a, and the beam size (aj×bj) of the j-th shot.

$\begin{matrix}{\mspace{79mu} \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack} & \; \\{d_{j} = {\frac{D_{j} \cdot \eta}{4}\left\{ {{{erf}\left( \frac{x_{i} - x_{j}}{\sigma} \right)} - {{erf}\left( \frac{x_{i} - x_{j} - a_{j}}{\sigma} \right)}} \right\} \left\{ {{{erf}\left( \frac{y_{i} - y_{j}}{\sigma} \right)} - {{erf}\left( \frac{y_{i} - y_{j} - b_{j}}{\sigma} \right)}} \right\}}} & (1)\end{matrix}$

In the temperature increase amount calculation step (S118), thetemperature increase amount calculation unit 62 calculates, under eachwriting condition, a temperature increase amount of the evaluationpattern 12 concerned, which is increased due to heat transferred from ashot previous to the shot concerned, at each shot time of a plurality ofshots for forming the peripheral pattern 14.

FIG. 10 shows an example of a calculation model for calculating atemperature increase amount at a shot position of interest (target shotposition), which is increased due to heat transferred from another shot,according to the first embodiment. In FIG. 10, it is supposed that heatis transferred from the j-th shot to the position (xi, yi) of the i-thtarget shot. Moreover, it is supposed that all the energies of shots ofelectron beams are distributed in a rectangular parallelepiped of shotsize. The depth direction size of the rectangular parallelepiped shallbe the range, called “Grun range” (Rg), (when acceleration voltage is 50kV, for example, it is 20 μm or less) in the glass substrate (quartz) ofan electron acquired from an experimental formula. The medium of heattransfer is a glass substrate only, and the light-shielding film and theresist are not take into consideration. In that case, a temperatureincrease amount δTij at the time t at the i-th shot position ofinterest, which is generated due to heat transfer from the j-th shot,can be defined by the equation (2) described below, using Grun range Rg,density ρ of a glass substrate, specific heat Cp of a glass substrate,acceleration voltage V, current density J, beam irradiation start timet_(j,1) of the j-th shot, beam irradiation finish time t_(j,2) of thej-th shot, coefficient k, beam irradiation time ti of the i-th shot ofinterest, time t concerned, position (xi, yi) of the i-th shot ofinterest, position (x_(j,1), y_(j,1)) at lower left corner of the j-thshot, and position (x_(j,2), y_(j,2)) at upper right corner of the j-thshot.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{{\delta \; T_{ij}} = {\frac{V \cdot J}{R_{g} \cdot \rho \cdot C_{p}}{\overset{t_{j,2}}{\int\limits_{t_{j,1}}}{{{{erf}\left( \frac{R_{g}}{\sigma^{\prime}} \right)} \cdot F}{t}}}}} & (2)\end{matrix}$

However, the function F in the equation (2) is defined by the followingequation (3).

$\begin{matrix}{\mspace{79mu} \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack} & \; \\{F = {\frac{1}{2}{\left\{ {{{erf}\left( \frac{x_{i} - x_{j,1}}{\sigma^{\prime}} \right)} - {{erf}\left( \frac{x_{i} - x_{j,2}}{\sigma^{\prime}} \right)}} \right\} \cdot \frac{1}{2}}\left\{ {{{erf}\left( \frac{y_{i} - y_{j,1}}{\sigma^{\prime}} \right)} - {{erf}\left( \frac{y_{i} - y_{j,2}}{\sigma^{\prime}} \right)}} \right\}}} & (3)\end{matrix}$

However, the function σ′ in the equations (2) and (3) is defined by thefollowing equation (4).

[Equation 4]

σ′=2√{square root over (k(t _(i) −t))}  (4)

Thus, a temperature increase amount Ti(t) at the shot position of thei-th shot of interest and at the time t concerned, which has beenincreased because of heat transferred from all the shots previous to thetime t concerned, is a sum of temperature increase amounts δTij at thei-th shot position of interest and at the time t, which are generateddue to heat transferred from each shot performed before the time t, canbe defined by the following equation (5).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack & \; \\{{T_{i}(t)} = {\sum\limits_{j = 0}{\delta \; T_{ij}}}} & (5)\end{matrix}$

Therefore, for each of a plurality of shots for forming the peripheralpattern 14, calculated is a temperature increase amount Ti(t) at thei-th shot position of interest and at the time t, which is generated dueto heat transferred from each shot performed before the time t at whichthe shot concerned is performed. Thereby, for each of a plurality ofshots for forming the peripheral pattern 14, a temperature increaseamount Tilt) at the time when a backscattered electron resulting fromthe shot concerned exposes the CD position of interest and at the CDposition of interest can be obtained.

In the correlation parameter calculation step (S120), the correlationparameter calculation unit 78 calculates a correlation parameter B fordefining the correlation among a width change amount ΔCD of theevaluation pattern 12, a temperature increase amount Ti(t) of theevaluation pattern 12, and a backscatter dose dj which reaches to theevaluation pattern 12, by using a width dimension CD of the evaluationpattern 12 under each writing condition, a temperature increase amountTi(t) of the evaluation pattern 12 concerned at each shot for theperipheral pattern 14 under each writing condition, and a backscatterdose dj to the evaluation pattern 12 from each shot for the peripheralpattern 14 under each writing condition.

FIG. 11 shows an example of a model of correlation according to thefirst embodiment. In FIG. 11, the ordinate axis represents a widthchange amount ΔCD of the evaluation pattern 12 (CD position of interest,target CD position). The abscissa axis represents a sum Σdj·Tj ofproducts each obtained by multiplying a backscatter dose dj, which isdue to the j-th shot reaching to the shot position i of interest, by atemperature Tj at the shot position i of interest and at the time of thej-th shot. The temperature Tj at the shot position i of interest and atthe time of the j-th shot is a temperature increase amount Ti(t) at theshot position of the i-th shot of interest and at the j-th shot time t,which has been increased because of all the shots previous to the j-thshot time t. Therefore, under each writing condition, the sum Σdj·Tj ofdj·Tj with respect to each shot for forming the peripheral pattern 14and the width change amount ΔCD of the evaluation pattern 12 (CDposition of interest, target CD position) are approximated by anapproximate expression. Here, for example, a primary expression is usedfor the approximation. The approximate expression can be defined by thefollowing equation (6).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack & \; \\{{\Delta \; {CD}} = {B{\sum\limits_{j}{d_{j} \cdot T_{j}}}}} & (6)\end{matrix}$

Therefore, the correlation parameter calculation unit 78 calculates acorrelation parameter B (parameter for dose correction of electron beam)for defining the correlation shown by the approximate expression, byusing Σdj·Tj and width change amount ΔCD under each writing condition.The calculated correlation parameter B is made to be related to a resisttype so as to be output to the storage device 144 and stored therein.The correlation is not limited to a primary expression, and a second orhigher order polynomial may also be used.

In the example described above, in order to obtain the correlationparameter B, the temperature Tj at the shot position i of interest ischanged by variably changing the settling time. However, it is notlimited thereto.

FIGS. 12A to 12C show another example of an evaluation pattern and aperipheral pattern according to the first embodiment. FIG. 12A shows anexample of the evaluation pattern 12 and the peripheral pattern 14surrounding the evaluation pattern 12. As shown in FIG. 12B, thedistance between the evaluation pattern 12 and the peripheral pattern 14can be changed by changing the inner side size of the peripheral pattern14 of FIG. 12A. The values of dj and Tj can be variable by changing thedistance between the evaluation pattern 12 and the peripheral pattern14. Moreover, as shown in FIG. 12C, the values of dj and Tj can bevariable by changing the dose used for writing the peripheral pattern 14defined in the chip B.

FIGS. 13A and 13B show another example of the evaluation pattern and theperipheral pattern according to the first embodiment. The value of Tjcan be variable by writing the evaluation pattern 12 defined in the chipA by each shot whose settling time is fixed in FIG. 13A, and making thesettling time of each shot for forming the peripheral pattern 14 definedin the chip B variable in FIG. 13B.

FIGS. 14A and 14B show another example of the evaluation pattern and theperipheral pattern according to the first embodiment. Although theexample described above shows the case where the combination of theevaluation pattern 12 and the peripheral pattern 14 surrounding theevaluation pattern 12 is used, the shape of the evaluation pattern 12and the peripheral pattern 14 is not limited thereto. As shown in FIG.14A, the evaluation patterns 12 a to 12 e may be configured as aplurality of line patterns extending in the same direction, and as shownin FIG. 14B, line patterns of the peripheral patterns 14 a to 14 e maybe respectively arranged between the line patterns configuring theevaluation pattern 12. Even in this configuration, it is possible tovariably change the values of dj and Tj.

FIGS. 15A to 15F show an example of a width dimension depending on thetype of resist according to the first embodiment. The relation betweenthe width dimension CD and the settling time described in FIGS. 7A and7B and FIGS. 8A and 8B are dependent on the type of resist. FIG. 15Ashows an example of the relation between the width dimension of anevaluation pattern and the settling time according to the comparativeexample (2) to the first embodiment, where multiple writing of threepasses is performed with the dose of 23.5 μC/cm², for example, using theresist A. FIG. 15B shows an example of the relation between the widthdimension of an evaluation pattern and the settling time according tothe first embodiment, where multiple writing of three passes isperformed with the dose of 23.5 μC/cm², for example, using the resist A.If standardization is performed by dividing the maximum dimension changeamount by the dose per pass, it is 0.217 nm/(μC/cm²) in the case ofusing the resist A in the example of FIG. 15A. It is 0.056 nm/(μC/cm²)in the case of using the resist A in the example of FIG. 15B.

FIG. 15C shows an example of the relation between the width dimension ofan evaluation pattern and the settling time according to the comparativeexample (2) to the first embodiment, where multiple writing of twopasses is performed with the dose of 15.1 μC/cm², for example, using theresist B. FIG. 15D shows an example of the relation between the widthdimension of an evaluation pattern and the settling time according tothe first embodiment, where multiple writing of two passes is performedwith the dose of 15.1 μC/cm², for example, using the resist B. Ifstandardization is performed by dividing the maximum dimension changeamount by the dose per pass, it is 0.397 nm/(μC/cm²) in the case ofusing the resist B in the example of FIG. 15C. It is 0.201 nm/(μC/cm²)in the case of using the resist B in the example of FIG. 15D.

FIG. 15E shows an example of the relation between the width dimension ofan evaluation pattern and the settling time according to the comparativeexample (2) to the first embodiment, where multiple writing of one pass(not multiplexed) is performed with the dose of 6.4 μC/cm², for example,using the resist C. FIG. 15F shows an example of the relation betweenthe width dimension of an evaluation pattern and the settling timeaccording to the first embodiment, where multiple writing of one pass(not multiplexed) is performed with the dose of 6.4 μC/cm², for example,using the resist C. If standardization is performed by dividing themaximum dimension change amount by the dose per pass, it is 0.734nm/(μC/cm²) in the case of using the resist C in the example of FIG.15E. It is 0.195 nm/(μC/cm²) in the case of using the resist C in theexample of FIG. 15F.

As described above, the relation between the width dimension CD and thesettling time depends on the type of resist. Therefore, according to thefirst embodiment, it is preferable to acquire a correlation parameter Bfor each resist type. The method for acquiring the correlation parameterB is what has been described above.

According to the first embodiment, as described above, it is possible toacquire, for each resist type, a correlation parameter B for performingdose correction for heating effect on backscattering. The correlationparameter B is made to be related to a resist type, and stored in thestorage device 144.

Although, in the example described above, after measuring the widthdimension CD, each calculation step up to calculating the correlationparameter B is performed in the writing apparatus 100, it is not limitedthereto. It is also preferable to perform the calculation in anarithmetic device outside of the writing apparatus 100. In that case,the calculated correlation parameter B for each resist type is inputfrom the outside of the writing apparatus 100, and stored in the storagedevice 144. In other words, there is stored, for each resist type, acorrelation parameter B for a width change amount ΔCD changed from adesign dimension of a figure pattern (shot figure), a temperatureincrease amount Tj of the figure pattern (shot figure), and abackscatter dose dj reaching to the figure pattern (shot figure) in thestorage device 144.

Next, a method of writing after performing dose correction for heatingeffect on backscatter by using the correlation parameter B will bedescribed.

FIG. 16 is a flowchart showing main steps of a writing method accordingto the first embodiment. As shown in FIG. 16, the writing methodaccording to the first embodiment executes a series of steps: a writingcondition setting step (S202), a shot data generation step (S204), adose calculation step (S206), an extraction step (S208), a setting step(S210), a backscatter dose calculation step (S212), a temperatureincrease amount calculation step (S214), a ΔCD calculation step (S216),a determination step (S218), a correction coefficient calculation step(S220), a dose correction step (S222), a determination step (S224), anda writing step (S226).

In the writing condition setting step (S202), the writing conditionsetting unit 50 reads writing condition information from the storagedevice 142, and sets, to the writing apparatus 100 (writing control unit74, for example), writing conditions for writing a chip pattern (aplurality of figure patterns) defined in the writing data stored in thestorage device 140. As an example of the writing conditions, settlingtime between a plurality of shots can be cited. Further, for example, adose, the number of passes (multiplicity) of multiple writing, the orderof writing of shots, the maximum shot size, etc. can be cited.

In the shot data generation step (S204), the shot data generation unit52 reads out writing data from the storage device 140, and performs dataconversion processing of several steps in order to generate shot dataunique to the writing apparatus 100. The size of each figure patterndefined in the writing data is usually larger than the maximum shot sizethat can be shot by the writing apparatus 100, and in many cases it isimpossible to form the figure pattern by one shot of the electron beam200. Therefore, each figure pattern is divided into a plurality of shotfigures each having the size equal to or less than the maximum shot sizethat can be shot of an electron beam. Then, shot data is generated foreach shot figure. As the shot data, the figure code indicating thefigure type of the shot figure concerned, coordinates to be irradiatedwith a shot, and the size of the shot figure are defined. Under thecontrol of the writing control unit 74, each shot data is rearranged inthe order of shots, and stored in the storage device 148. Shot data iscalculated for each stripe region, for example.

In the dose calculation step (S206), the dose calculation unit 54 readsout writing data from the storage device 140, and calculates a dose Dfor each mesh region of a predetermined size. As the calculation methodfor obtaining the dose D, a conventional method can be used. The dose Dcan be calculated by multiplying a base dose Dbase by a correctioncoefficient. It is preferable to use as the correction coefficient, forexample, a proximity effect correction coefficient. Since the influenceradius (backscatter radius σ) of the proximity effect is several μm to10 μm, it is preferable for the size of a mesh for correcting thefogging-effect to be approximately 1/10 of the influence radius, forexample, to be 0.5 μm to 1 μm in order to perform correctioncalculation. In addition, in order to correct the dose, it is alsopreferable to use an irradiation coefficient for the fogging effectcorrection, a correction coefficient for loading correction, etc. Thedose calculation unit 54 generates a dose map in which each calculateddose is defined for each region. The generated dose map is stored in thestorage device 148. The dose map is calculated for each stripe region,for example. In the dose map, each dose being a map value is preferablydefined in the state having been converted into an irradiation time. Theirradiation time can be defined by dividing a dose D by a currentdensity J.

In the extraction step (S208), the resist information extraction unit 58extracts, from the storage device 142, information on the type of resistcoated on the target object 101 serving as a writing target substrate.

In the setting step (S210), the setting unit 56 sets a shot of interest(target shot) in the order of writing, for example.

In the backscatter dose calculation step (S212), the backscatter dosecalculation unit 60 calculates a backscatter dose dj, which reaches tothe shot position of the shot figure (figure pattern) of a shot ofinterest from each shot of a plurality of shots of the electron beam 200in the case where the shot position of the shot figure of the shot ofinterest exists in the influence range of the proximity effect of eachof the plurality of shots. As the method for calculating the backscatterdose dj, the equation (1) described above can be used. As the dose ofeach shot used for the calculation, the dose at the position concernedin the dose map stored in the storage device 148 is used. Further, asthe backscatter dose dj reaching to the irradiation position of the shotof interest from the beam shot at the shot position irradiatedpreviously to the shot of interest, it is more preferable to use a dosehaving been corrected in the dose correction step (S222) to be describedlater.

In the temperature increase amount calculation step (S214), thetemperature increase amount calculation unit 62 calculates a temperatureincrease amount Tj at the shot position of the shot figure (figurepattern) of the shot of interest and at the time of the shot ofinterest, which is increased due to heat transferred from another shot,for each of a plurality of shots in the case where the shot position ofthe shot figure (figure pattern) of the shot of interest exists in theinfluence range of the proximity effect of each of the plurality ofshots. Here, the “another shot” indicates all the shots having beenperformed at the time of shot whose backscattered electron reaches tothe shot position of the shot of interest, regardless of the range ofthe proximity effect. However, a shot emitted from the position beingtoo distant to transfer heat to the shot position of the shot ofinterest may be removed from the calculation targets. As the method forcalculating the temperature increase amount Tj, the equations (2) to (5)described above should be used.

In the ΔCD calculation step (S216), the ΔCD calculation unit 64 readsout a correlation parameter B corresponding to an extracted resist typefrom the storage device 144 which stores, for each resist type, acorrelation parameter B for the width change amount ΔCD of a figurepattern, the temperature increase amount Tj of the figure pattern, andthe backscatter dose dj reaching to the figure pattern, and whenwriting, using the electron beam 200, a figure pattern under the writingconditions (predetermined writing conditions) having been set,calculates the width change amount ΔCD of the figure pattern concernedby using the correlation parameter B. Specifically, the ΔCD calculationunit 64 calculates the width change amount ΔCD of the shot figure(figure pattern) of the shot of interest, by using a temperatureincrease amount Tj at the shot position of the shot figure (figurepattern) of the shot of interest at each shot time of each shot whosebackscattered electron reaches to the shot position of the shot ofinterest, a backscatter dose dj reaching from the shot concerned to theshot position of the shot figure (figure pattern) of the shot ofinterest at each shot time of each shot whose backscattered electronreaches to the shot position of the shot of interest, and a correlationparameter B. As the method for calculating a width change amount ΔCD,the equation (6) described above should be used.

In the determination step (S218), the determination unit 53 determines,using the width change amount ΔCD, whether it is necessary to correctthe dose of the electron beam 200 of the shot of interest when writing,under the writing conditions (predetermined writing conditions) havingbeen set, the shot figure (figure pattern) of the shot of interest byusing the electron beam 200. Specifically, the determination unit 53determines whether the calculated width change amount ΔCD of the shotfigure (figure pattern) of the shot of interest is in an allowablerange. If the calculated width change amount ΔCD is in the allowablerange, it proceeds to the determination step (S224) without correctingthe dose. If the calculated width change amount ΔCD is out (larger) ofthe allowable range, it proceeds to the correction coefficientcalculation step (S220).

In the correction coefficient calculation step (S220), the correctioncoefficient calculation unit 68 calculates a correction coefficient kfor correcting the dose of the electron beam for writing the shot figure(figure pattern) of the shot of interest when it is determined thatcorrection of the dose is needed. The correction coefficient k iscalculated so that the width change amount ΔCD of the shot figure(figure pattern) of the shot of interest which has been calculated usingthe correlation parameter B may be corrected.

FIG. 17 shows an example of a relation between the width dimension andthe dose according to the first embodiment. In FIG. 17, the ordinateaxis represents a width dimension CD, and the abscissa axis represents adose D. The relation between the width dimension CD and the dose D canbe obtained in advance by experiment etc. This relation should beobtained for each pattern density p. For example, it is recommended toobtain the relation with respect to the cases of ρ≈0, ρ=0.5 (50%), andρ=1 (100%). Then, the relation in the case of an applicable patterndensity should be obtained by linear interpolation. Then, the correctioncoefficient calculation unit 68 calculates a correction coefficient k byusing which a dose D₀ having been calculated in the dose calculationstep (S206) to form a width dimension CD₀ is corrected to a dose D(=kD₀) corresponding to the position obtained by correcting the widthdimension CD₀ by the width change amount ΔCD.

In the dose correction step (S222), the correction unit 70 corrects,using the correction coefficient k, the dose D of the electron beam 200for writing the shot figure (figure pattern) of the shot of interest.The corrected dose D is overwritten in the dose map stored in thestorage device 148. The size of the map value of the dose map is set tobe larger than the shot size. Therefore, different doses may be definedwith respect to the same map value. Thus, the dose for each shotposition is to be defined as attribute data for each map value.

In the determination step (S224), the determination unit 72 determineswhether each calculation processing from the setting step (S210) to thedose correction step (S222) described above has been completed for allthe shots in the stripe region concerned. When having been completed, itproceeds to the writing step (S226). When there remains a shot beforebeing processed, it returns to the setting step (S210), and each stepfrom the setting step (S210) to the determination step (S224) isrepeated until calculation processing has been completed for all theshots.

In the writing step (S226), the writing unit 150 writes, under thewriting conditions (predetermined writing conditions) having been set,the shot figure (figure pattern) of each shot on the target object 101(substrate) by using the electron beam 200 of the corrected dose.Specifically, it operates as described below. The deflection controlcircuit 120 acquires an irradiation time from the dose map stored in thestorage device 148. Then, the deflection control circuit 120 outputs adigital signal for controlling the irradiation time of each shot to theDAC amplifier unit 130. The DAC amplifier unit 130 converts the digitalsignal into an analog signal to be amplified and applied as a deflectionvoltage to the blanking deflector 212.

With respect to the electron beam 200 emitted from the electron gun 201(emitter), when passing through the blanking deflector 212, it iscontrolled to pass through the blanking aperture 214 by the blankingdeflector 212 when in the beam ON state, and the whole of it isdeflected to be blocked by the blanking aperture plate 214 when in thebeam OFF state. The electron beam 200 that has passed through theblanking aperture plate 214 during the period from changing a beam OFFstate to a beam ON state to changing the beam ON state to a beam OFFstate serves as one shot of the electron beam. The blanking deflector212 controls the direction of the passing electron beam 200 toalternately generate a beam ON state and a beam OFF state. For example,when in a beam ON state, no voltage is applied to the blanking deflector212, and, when in a beam OFF state, a voltage should be applied to it.The dose per shot of the electron beam 200 to irradiate the targetobject 101 is adjusted depending upon the irradiation time of each shot.

As described above, each shot of the electron beam 200, generated bypassing through the blanking deflector 212 and the blanking apertureplate 214, irradiates the whole of the first shaping aperture plate 203which has a quadrangular opening by the illumination lens 202. At thisstage, the electron beam 200 is first shaped to a quadrangle. Then,after passing through the first shaping aperture plate 203, the electronbeam 200 of the first aperture image is projected onto the secondshaping aperture plate 206 by the projection lens 204. The firstaperture image on the second shaping aperture plate 206 isdeflection-controlled by the deflector 205 so as to change (variablyshape) the shape and size of the beam. Such variable beam shaping isperformed for each shot, and, generally, each shot is shaped to have adifferent shape and size. Then, after passing through the second shapingaperture plate 206, the electron beam 200 of the second aperture imageis focused by the objective lens 207, and deflected by the maindeflector 208 and the sub deflector 209 to reach a desired position onthe target object 101 placed on the XY stage 105 which movescontinuously. As described above, a plurality of shots of the electronbeam 200 are deflected in order, by each deflector, onto the targetobject 101 serving as a substrate.

As described above, according to the first embodiment, it is possible toacquire a parameter B for performing dose correction for heating effectof backscattering. Therefore, patterns can be written in highly precisedimensions.

Embodiments have been explained referring to specific examples describedabove. However, the present invention is not limited to these specificexamples.

While the apparatus configuration, control method, and the like notdirectly necessary for explaining the present invention are notdescribed, some or all of them can be selectively used on a case-by-casebasis when needed. For example, although description of theconfiguration of the control unit for controlling the writing apparatus100 is omitted, it should be understood that some or all of theconfiguration of the control unit can be selected and used appropriatelywhen necessary.

In addition, any other method of acquiring a parameter for performingdose correction of a charged particle beam, charged particle beamwriting method, and charged particle beam writing apparatus that includeelements of the present invention and that can be appropriately modifiedby those skilled in the art are included within the scope of the presentinvention.

Additional advantages and modification will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A method for acquiring a parameter for correcting a dose of a charged particle beam comprising: writing, using a charged particle beam, a plurality of evaluation patterns on a substrate coated with resist; writing, under each writing condition while varying writing condition for each of the plurality of evaluation patterns, a peripheral pattern according to a corresponding writing condition on a periphery of any different one of the plurality of evaluation patterns by using a plurality of shots of the charged particle beam, after time that can be disregarded with respect to influence of temperature increase of the resist due to writing of an evaluation pattern concerned of the plurality of evaluation patterns has passed; measuring, under the each writing condition, a width dimension of the evaluation pattern concerned, on whose periphery the peripheral pattern has been written; calculating, under the each writing condition, a backscatter dose reaching the evaluation pattern concerned from each shot of the plurality of shots; calculating, under the each writing condition, a temperature increase amount of the evaluation pattern concerned, which is increased due to heat transferred from at least one shot previous to a shot concerned in the plurality of shots, at each shot time of the plurality of shots; and calculating a correlation parameter for defining a correlation among a width dimension change amount of the evaluation pattern concerned, the temperature increase amount of the evaluation pattern concerned, and the backscatter dose reaching to the evaluation pattern concerned, by using a width dimension of the evaluation pattern concerned under the each writing condition, the temperature increase amount of the evaluation pattern concerned at the each shot time under the each writing condition, and the backscatter dose reaching the evaluation pattern concerned from the each shot under the each writing condition, and outputting the correlation parameter.
 2. The method according to claim 1, wherein the correlation parameter is acquired for each type of the resist.
 3. The method according to claim 1 further comprising: generating, using first chip data which defines pattern data of the plurality of evaluation patterns, first shot data by performing data conversion processing of several steps for the first chip data; and generating, using second chip data which defines pattern data of the peripheral pattern, second shot data by performing data conversion processing of several steps for the second chip data, wherein the plurality of evaluation patterns are written using the first shot data generated, the second shot data is generated after the plurality of evaluation patterns have been written, and the peripheral pattern is written using the second shot data generated.
 4. The method according to claim 1, wherein the each writing condition is made variable by varying a settling time of an amplifier for applying a voltage to a deflector which deflects the charged particle beam.
 5. The method according to claim 1, wherein the each writing condition is made variable by varying a distance between the evaluation pattern concerned and the peripheral pattern.
 6. A charged particle beam writing method comprising: extracting information on a type of resist coated on a writing target substrate; reading out a corresponding correlation parameter which corresponds to the resist of an extracted type from a storage device which stores, for each type of the resist, a correlation parameter for a width dimension change amount of a figure pattern, a temperature increase amount of the figure pattern, and a backscatter dose reaching the figure pattern, and calculating the width dimension change amount of the figure pattern by using the correlation parameter when writing the figure pattern under a predetermined writing condition by using a charged particle beam; determining, using the width dimension change amount, whether it is necessary to correct a dose of the charged particle beam when writing, under the predetermined writing condition, the figure pattern by using the charged particle beam; calculating a correction coefficient for correcting the dose of the charged particle beam for writing the figure pattern when it is determined that correction of the dose is needed; correcting, using the correction coefficient, the dose of the charged particle beam for writing the figure pattern; and writing, under the predetermined writing condition, the figure pattern on the writing target substrate by using the charged particle beam of the dose having been corrected.
 7. The method according to claim 6 further comprising: calculating the backscatter dose which reaches a shot position of the figure pattern from each of a plurality of shots of the charged particle beam in a case where the shot position of the figure pattern exists in an influence range of a proximity effect due to the each of the plurality of shots; and calculating the temperature increase amount at the shot position of the figure pattern, which is increased due to heat transferred from another shot, at each shot time of the plurality of shots, wherein the width dimension change amount of the figure pattern is calculated using the temperature increase amount at the shot position of the figure pattern at the each shot time, the backscatter dose reaching from a shot concerned at the each shot time to the shot position of the figure pattern, and the correlation parameter, and the correction coefficient is calculated so that the width dimension change amount of the figure pattern which has been calculated using the correlation parameter is corrected.
 8. The method according to claim 6, wherein the backscatter dose and the temperature increase amount at the shot position of the figure pattern at reaching time of the backscatter dose are calculated whenever the backscatter dose resulting from another shot reaches the shot position of the figure pattern, and the width dimension change amount of the figure pattern is calculated using a sum of products of the backscatter dose with respect to all of the another shot whose backscatter dose reaches the shot position of the figure pattern, and the temperature increase amount at the reaching time.
 9. A charged particle beam writing apparatus comprising: an extraction processing circuitry configured to extract information on a type of resist coated on a writing target substrate; a storage device configured to store, for each type of the resist, a correlation parameter for a width dimension change amount changed from a design dimension of a figure pattern, a temperature increase amount of the figure pattern, and a backscatter dose reaching the figure pattern; a width dimension change amount calculation processing circuitry configured to read out a corresponding correlation parameter which corresponds to an extracted type of the resist from the storage device, and to calculate the width dimension change amount of the figure pattern by using the correlation parameter in a case of writing the figure pattern under a predetermined writing condition by using a charged particle beam; a determination processing circuitry configured to determine, using the width dimension change amount, whether it is necessary to correct a dose of the charged particle beam in the case of writing, under the predetermined writing condition, the figure pattern by using the charged particle beam; a correction coefficient calculation processing circuitry configured to calculate a correction coefficient for correcting the dose of the charged particle beam for writing the figure pattern in a case where it is determined that correction of the dose is needed; a correction processing circuitry configured to correct, using the correction coefficient, the dose of the charged particle beam for writing the figure pattern; and a writing mechanism configured to include a stage for mounting the writing target substrate thereon, an emission source for emitting charged particle beams, and a deflector for deflecting the charged particle beams, and to write, under the predetermined writing condition, the figure pattern on the writing target substrate by using the charged particle beam of the dose having been corrected.
 10. The apparatus according to claim 9 further comprising: a backscatter dose calculation processing circuitry configured to calculate the backscatter dose reaching a shot position of the figure pattern from each of a plurality of shots of the charged particle beam in a case where the shot position of the figure pattern exists in an influence range of a proximity effect of the each of the plurality of shots; and a temperature increase amount calculation processing circuitry configured to calculate the temperature increase amount at the shot position of the figure pattern, which is increased due to heat transferred from another shot, at each shot time of the plurality of shots, wherein the width dimension change amount calculation processing circuitry calculates the width dimension change amount of the figure pattern by using the temperature increase amount at the shot position of the figure pattern at the each shot time, the backscatter dose reaching from a shot concerned at the each shot time to the shot position of the figure pattern, and the correlation parameter, and the correction coefficient calculation processing circuitry calculates the correction coefficient so that the width dimension change amount of the figure pattern which has been calculated using the correlation parameter is corrected. 